It is well known in the art that PET is useful for many packaging applications. It is also very well known and practiced that PET or modified PET is the polymer of choice for making beverage and food containers, particularly carbonated beverage containers. Furthermore, it is known that PET can be modified, on a commercial scale with either CHDM or isophthalic acid (or dimethyl isophthalate).
While each comonomer has its benefits, both suffer from detriments when used alone. CHDM improves the ease of processing of the resin, but unfortunately decreases the barrier properties of the resultant container. Isophthalic acid increases the barrier of the PET, but unfortunately decreases the processing window in which acceptable containers can be formed. Accordingly, there remains a need in the art for a resin which displays improved barrier without sacrificing processability.
WO 98/02479 discloses copolyesters containing repeat units from terephthalic acid, ethylene glycol, at least 5 mole % isophthalic acid and optionally 2,6-naphthalene dicarboxylic acid. However, additional repeat units, such as CHDM are not disclosed.